Encapsulant layers for photovoltaic (PV) modules are typically made of ethylene vinyl acetate (EVA) resin. PV modules can include crystalline silicon wafers that are connected together and embedded in a laminating film. The laminating film and the embedded wafers are typically sandwiched between two layers (or panels) of glass, a polymeric material, or other suitable materials. PV modules can also include amorphous silicon, cadmium-telluride (CdTe) or copper-indium-diselenide, CuInSe2 (commonly referred to as “CIS”), or a similar semiconductor material deposited as a thin film on a substrate by well known physical vapor deposition (“PVD”) or chemical vapor deposition (“CVD”) techniques. To complete the construction, the layers are etched and an adhesive is applied over the etched PV cell. A backing material is then applied over the assembly adhesive.
Typically, two encapsulant layers are used, one below and one above the etched PV cell, to provide moisture, oxygen, and electrical isolation to the cell. The encapsulant layer that covers the face of the cell is typically transparent. The other encapsulant or “back sheet” is disposed on a “substrate” layer such as a trilayer PVF/PET/PVF (TPT) laminate sheet or other adequate polymer backsheets. A metal or polyimide film have been used, adjacent to the back sheet to provide further protection against outside influences, such as moisture. Additional details of PV modules and their construction methods can be found in U.S. Pat. No. 5,508,205; U.S. Pat. No. 6,066,796; U.S. Pat. No. 6,420,646; U.S. Pat. No. 7,449,629; US 2008-0245405; US 2008-0276983; US 2009-0101204; US 2009-0162666; and WO 2007-002618, for example.
To increase production or lower the cost of production of PV modules, producers are continually trying to increase output rates or decrease reaction temperatures needed to laminate the EVA resin encapsulant layer on the PV cell assembly. For example, producers have used higher amounts of peroxide crosslinking agents or peroxide crosslinking agents at lower temperatures. Producers have also tried peroxides with two or more reactive sites (reacting with different activation energies), and/or mixes of low and high temperature crosslink agents. Producers have further tried crosslink enhancers such as tri-allyl isocyanurate (TAIC) to increase the crosslinkability of the EVA resin, which reduces the lamination times. Such post-polymerization conversions are very time consuming and/or costly. It is much more desirable to produce a neat EVA resin with an increased intrinsic crosslinkability to increase production rates of PV modules.
There is a need, therefore, for an improved EVA resin with increased crosslinkability and processes for making the same.